A Study in Parallel Universes: the Weakless Universe

No weak force.

I haven’t written about my work much on this blog. I’ve mostly kept to interesting science stories in the news or the community, but since this is a website for science as well as science fiction, I wanted to talk about a new paper that I have written with fellow physicists Evan Grohs and Fred Adams here at the University of Michigan, exploring the idea of a “weakless universe”—a universe without the weak nuclear force. It has been accepted for publication by Physical Review D and is available to the public to read here.

Now, the first question you might be asking is, why would we study parallel universes? To be sure, this is a purely theoretical study of something that, even if it existed, would probably never be observable. However, there are good reasons for this. First, just as you will often learn more about your native tongue by studying a foreign language, thinking about what other universes might be like helps us better understand our own. And second, it addresses a small part of a longstanding philosophical question in physics: does the universe have to look the way it does in order for life to exist?

The “weakless universe” is a universe without the weak nuclear force (also called the “weak force”), one of the four fundamental forces of nature. Usually, we say that the weak force causes radioactive decay, but there’s more to it than that. The weak force drives two very important cosmic processes: the fusion of hydrogen to helium in the sun, and the explosion of supernovae, which distribute heavy elements across the universe. If you remove the weak force, it seems that there would be no stars, and even if there were stars, the universe wouldn’t have the necessary elements to produce life. Or would it?

The idea of a weakless universe was first studied by a team of particle physicists in Harnik, Kribs, & Perez (2006), who suggested that such a universe could support life, producing the necessary elements by different processes. The idea enjoyed a bit of popular attention in a 2009 Scientific American article, but their analysis was incomplete and didn’t dig deep into the mechanics of how stars would operate without a weak force. We decided to follow up on their work to create a more complete picture of such a universe, and we found that it would look different in some key ways, but it could still support life as we know it.

To start off, without the weak force, neutrons, which normally decay into protons on their own, are stable. Many radioactive isotopes—all those that decay by beta decay like carbon-14 and strontium-90, are also stable (but not uranium and plutonium, which decay by alpha decay). Because of this, instead of the Big Bang producing many more protons than neutrons, as in our universe, the weakless universe produces them in roughly equal numbers. By itself, this would result in nearly all the matter in the universe fusing into helium in the Big Bang, which is not good for life.

The solution is to change one other thing: the density of the universe—or more specifically, η (pronounced “eta”), the density of protons and neutrons in the universe. If there are fewer particles around, they can avoid colliding and fusing together in the early universe. Galaxies are big, so there’s still plenty of gas around to form stars, but it’s not all helium.

The next problem is that the weakless universe has a bunch of free protons and free neutrons flying around. A proton and a neutron can fuse together into deuterium, and because they don’t electrically repel each other, they don’t need a hot star to do it. It can happen in the cold of space. But space is also pretty empty. The question is how dense does this cosmic gas of protons and neutrons need to be to fuse into deuterium quickly. That’s something we can calculate, and it turns out to be the density of a forming protostar. Stars will be going through nuclear fusion before they form.

This early fusion doesn’t stop star formation because fusing protons and neutrons into deuterium only produces a little bit of energy, but it does mean that stars will be made almost entirely out of deuterium. In fact, this solves one of our original problems: the hydrogen fusion in the Sun doesn’t work without the weak force, but deuterium fusion does. It uses the strong force.

Deuterium burns much faster than normal hydrogen, and at a lower temperature. Deuterium stars in a weakless universe will switch on before they fully collapse, when they are still big and red. A star with the mass of the Sun in a weakless universe would look a lot like a red giant, and it would last about as long as a red giant—only a few hundred million years, too short for life to develop as it did on Earth.

However, deuterium stars can also burn if they are smaller than stars in our universe, and smaller stars live longer. In our paper, we created a model of a “Weakless Sun”, which is only 5.6% the mass of our Sun (stars in our universe have to be at least 8% the mass of the Sun) and lives for close to 10 billion years. The Weakless Sun would look like a red dwarf, but brighter—about as bright as a K8 or K9 star in our universe, which puts it out of that worrisome M-dwarf territory where habitable planets would be tidally locked.

So we have long-lived stars. What about planets and life? Our other problem is that core-collapse supernovae don’t work, and those are the main source of oxygen and several other important elements in our universe. Luckily, there are two other processes that produce elements heavier than helium that do work: Type Ia supernovae, and red giant winds.

Type Ia supernovae are caused by exploding white dwarfs, which will exist in a weakless universe, are the main source of iron. They undergo nuclear fusion using the strong force, producing lots of iron and nickel, and also silicon, sulfur, and calcium, among others. Meanwhile, red giant stellar winds blow huge amounts of gas out into space, including the elements produced in their cores (known as “dredge-up”). Helium burning in red giants produces mostly carbon, but also some oxygen—not as much as our universe, but some.

Now, we’ve got iron and silicon to form planets; and we also have carbon, hydrogen, and oxygen, the minimum elements needed to form life as we know it. We’re short on nitrogen; there’s some around, but a lot less than in our universe, which complicates matters, but it doesn’t forbid life from occurring. It might just have to evolve differently. The bottom line is that life would be harder to form in a weakless universe, but contrary to our initial guess, it’s still possible, and I think that’s pretty cool. As Fred Adams would say, it’s a lot harder than we think to “break the universe”, and that includes even getting rid of one of the fundamental forces.

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What If? Rejects #12.2: Resonant Frequency

Image result for cat airplane

Previous post in this series: Ticks

And here it is! The final rejected question from xkcd writer Randall Munroe’s book, What If? It’s been a crazy ride.

Q: Assuming a relatively uniform resonant frequency in a passenger jet, how many cats, meowing at what resonant frequency of said jet, would be required to “bring it down”?

Randall’s response: “Hello, FAA? Is there a ‘Brittany’ [submitter] on the No-Fly List? …Yes, with cats. That sounds like her. Ok, just making sure you were aware.”

My response: I’m not sure why “bring it down” is in quotation marks.

The wording of this problem asks us to make two pretty big assumptions: that a passenger jet will have a uniform resonant frequency, and that it will vibrate freely enough that bombarding it with sound waves will damage it. At first, these seem like questionable assumptions. Shouldn’t airplanes be designed better than that? But no, it’s actually not crazy. Flutter is just such an oscillation, usually a bending of an airplane’s wings and fuselage that can occur when it is buffeted by turbulence and which can destroy a plane in extreme cases. Engineers will mitigate it, but it’s simply not possible to design wings to fully resist those forces.

In fact, this has happened before multiple times. Braniff Flight 542 in 1959 and Northwest Orient Flight 710 in 1960 both broke up in midair due to turbulence-induced flutter causing their wings to snap off, despite both being a then-new type of plane designed to eliminate flutter. In airplanes, resonant frequencies can be deadly.

So the premise is—disturbingly—plausible. Now, how does it relate to cats? This NASA study examined the resonant frequencies of aircraft wings and found a range of frequencies between 2 Hz and 50 Hz. That is not the frequency of meowing cats. These are deep bass notes at best. The lowest bass note in the standard opera repertoire is a low D at 73 Hz. Only the most extreme Russian composers pushed down to the G below low C at 49 Hz. This “plot” isn’t going to work with cats meowing. It’s going to need cats purring.

Domestic cats purr at different frequencies, but they average around 22 Hz, right in the middle of the resonant frequencies of airplane—a sound that’s more felt than heard by human ears. And this is a problem because while cats can meow at a potentially worrying 93 decibels, the loudest recorded purr is only 67.8 decibels, not much louder than your television. 70 decibels is a sound power level of only 0.00001 watts per cat, which is just not enough to do any serious damage to a plane, no matter how many you have. And that’s if you can get them all to purr at the same frequency, and that would be like, well, herding cats.

The bottom line is, you’re only going to bring down a passenger jet with cats if you load so many on that you put it over its weight limit.

How many is that, you ask? Well, the Airbus A320, the most popular passenger jet in the world, has a maximum cargo capacity of 44,100 pounds. Given the average weight of a house cat of 9 pounds, that’s 4,900 cats.

And now you’re back to the herding cats problem. That’s probably for the best.

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How The Last Jedi Fixes Star Wars; Yes, I Said It.

Image result for the last jedi boy with broom

I wrote before that I believe Star Wars: The Last Jedi redeemed the franchise in several important ways. This is a complicated topic, but I want to try to give you an outline of my thoughts.

To talk about The Last Jedi “redeeming” Star Wars, I’m speaking in the context of a little book called Star Wars on Trial by David Brin (and his other writings on the subject), in which he levels some pretty serious criticisms against the franchise, not least by calling Yoda the true villain of the series.

Brin is one of my favorite authors, but you have to understand when delving into his essays that he is wildly anti-Romantic (the intellectual movement of Romanticism, that is), and what he would probably call anti-feudalist. Personally, I think he goes a little too far the other direction, but he makes some good points.

Spoilers Ahoy!

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What If? Rejects #12.1: Ticks

Adult deer tick.jpg

Previous post in this series: Fire Tornados!

Next post in this series: Resonant Frequency

Q: What if I swallow a tick that has Lyme disease? Will my stomach acid kill the tick and the borreliosis, or would I get Lyme disease from the inside out?

Randall’s response: “Just to be safe, you should swallow something to kill the tick, like Solenopsis geminata (tropical fire ant). Then, swallow a Pseudacteon curvatus fly to kill the ant. Next, find a spider…

My response: I’m going to be honest…I’ve got nothing here.

I tried looking up the pH tolerance of Borrelia bacteria and didn’t find much. Then I tried to look up whether Borrelia is ever found in the stomach, and I got a big mess of claims, very few of which I actually trust.

Lyme disease is a complicated beast. It can be hard to diagnose, hard to treat, and symptoms can linger for months even after successful treatment. It can cause wide-ranging symptoms, and it attracts a lot of quacks. Websites claim that Lyme disease can mask itself as a bunch of other diseases, including stomach problems, and it is absolutely true that it can really screw up your liver. There is a worrying about of overlap between websites blaming Lyme for everything under the sun and websites offering alternative remedies and/or claiming to support the unrecognized diagnosis of “chronic Lyme disease”.

Advocates of the chronic Lyme disease hypothesis claim that Lyme disease is often not wiped out by a normal course of antibiotics and can linger for months or years and can cause any number of symptoms, including many symptoms not seen with a typical Lyme diagnosis. Opponents point to studies that indicate that “chronic Lyme” sufferers either have the well-known “post-treatment Lyme disease syndrome,” without an ongoing infection, or they simply never had Lyme in the first place and have had a misdiagnosis of chronic fatigue syndrome or something similar. They have also raised the alarm of the claimed chronic Lyme disease contributing to the overuse of antibiotics.

So the bottom line is, I don’t know. There are a lot of claims out there, and I don’t know enough about medicine to separate the truth from the pseudoscience. I’ll just note that we know Borrelia is carried in the tick’s stomach to infect humans, so I have feeling that swallowing it isn’t going to end well for you.

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Movie Review: Star Wars: The Last Jedi


Well, Star Wars Episode VIII is here, and it’s proving to be not only the biggest movie of the year, but also one of the most controversial. Not in the news headlines, that is, but quietly, in the actual audience reaction. Rotten Tomatoes rates The Last Jedi at 93% fresh from the critics, but only 56% from the audience. Why? Well, that’s complicated, but I think a big part of it is that it changed the “flavor” or style from the original Star Wars.

My opinion, though: I really liked it. Yes, the style was different. A friend of mine put it more lucidly than I ever could when he said, “It had a little too much Marvel in it.” But despite this, I really liked The Last Jedi. I honestly thought it was the best Star Wars movie yet. Yes, they changed the tone some, but I think, dare I say it, that those changes were necessary and made for a better movie and a better franchise.

My rating: 5 out of 5.

Spoilers below.

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What If? Rejects #11.2: Fire Tornadoes!

Previous post in this series: Moving an Island

Next post in this series: Ticks

Q: Are fire tornadoes possible?

Randall’s response: “YES. Fire tornadoes are a real thing that actually happens. Nothing I say could possibly add to this.”

My response: ‘Nuff said.

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Television Review: The New Mythbusters

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The Discovery Channel’s wildly popular MythBusters series ended in 2016, but it turned out that the show just couldn’t stay away. The Science Channel picked it up again, airing a game show to choose the new hosts of the series. Last month, the new MythBusters, Jonathan Lung and Brian Louden, started their own run of the show with plenty of all-new myths to explore.

I have to say, I don’t think the new MythBusters lives up to the standard set by Adam and Jamie. The show feels unpolished, and while Jon and Brian are fun, they don’t have the chemistry Adam and Jamie did. Now, part of this is probably inexperience. Jon and Brian are new and don’t have the ten years of mythbusting under their belts that their predecessors did. If you went back to the early seasons of the show, you would probably see some lower-quality work there, too.

What worries me a bit more is what I feel like is a drop in the scientific rigor and thinking of the new show. Adam and Jamie sometimes had this problem, too (don’t get me started on some of the driving myths), and to be honest, I felt that their final season was also lacking in fact-checking and well-thought-out conclusions, and it’s not all the new hosts’ faults.

It’s hard to say precisely why I feel the show has lost something in the transition. It’s little things like not doing the (fairly easy) math to find the correct fuel-air mixture for the chimney cannon (it makes sense in context) and failing to properly account for the order effect in the road rage myth, not to mention using a much smaller sample size than they used to. I’m just seeing some red flags here.

Still, it’s early, and I’m hopeful that Jon and Brian will learn over time as Adam and Jamie did. They’re off to a shaky start, but the show it still entertaining and worth watching, and with its strong history, I’m optimistic for its future.

My rating: 3.5 out of 5.

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